Fix SWITCH-MARK-WORK off-by-one: was tripping vm->error on every MSG-SEND (FABRIC-3.md §XXVIII.2)

mama_word_switch_mark_work()'s stack-underflow guard checked dsp < 2,
requiring 3+ items, when it only ever needs the 2 IDX>NAME leaves it
(caddr u). Since dsp is index-based (2 items == dsp 1), this rejected
every normal call. MSG-SEND tail-calls SWITCH-MARK-WORK unconditionally,
so this fired on every message sent anywhere in the system -- visible
only where a caller happened to check the target VM's error flag
afterward (mama_word_vm_exec()'s "VM-EXEC: ERROR in Artemis" report).

Verified clean on all 3 architectures: boot reaches Startup: Artemis
live -> zuse@Hera] ok> with no VM-EXEC: ERROR line at all.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BWpNjdwPtFLuVLaAq44L9K

capsules/BLOCK_MAP.md

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 # Capsule Block Manifest — Auto-generated
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+<!-- Generated by mkcapsule --manifest  2026-09-15T00:05:32Z -->
 <!-- DO NOT EDIT — re-run mkcapsule --manifest to refresh.  -->
 <!-- Hand-written justifications and immutability notes live  -->
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